It is generally known in the filtration art to equip a fluid supply line with a filter unit to remove impurities from the fluid flowing therethrough. It is also known in the art to utilize a fixed filter mounting head in the supply line and employ a replaceable filter cartridge which may be easily connected to and disconnected from the fixed mounting head.
Examples of such replaceable filter cartridge and head assemblies may be found in U.S. Pat. Nos. 3,746,171, 4,735,716 and 4,915,831. The filter assembly shown in U.S. Pat. No. 3,746,171 employs an external locking collar to secure the filter cartridge to the mounting head and provides a manually operated shut-off valve to block the flow of fluid through the head when the filter cartridge is being replaced. The filter assemblies disclosed in the U.S. Pat. No. 4,735,716 and U.S. Pat. No. 4,915,831 patents employ filter cartridges having a bayonet type connection to the mounting head but utilize one axial and one radial flow passage into the cartridge. The latter patent also includes a manually movable detent to prevent removing the filter cartridge from the mounting head until the fluid flow is turned off.